FI56320C - FOERFARANDE FOER ATT REDUCERA DEN TOTALA SVAVELHALTEN I AVGASER VID EN CLAUSPROCESS - Google Patents

Description

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C (45) Patent granted ΙΟ OI 1930 Patent neddelat '(51) Ky.lk. * / Lr * t.CI.' B 01 D 53 / 14- C 10 I 1/34 FINLAND-FINLAND (21) Patmttlhtkemuf - Pttentaroöknlng 2009/71. - (22) H »k« mi »p * lvi —An * ökntnpd« g 15.07.71 * * (23) Alkupiivl - Glltlghatidag 15,07.71 (41) Become Public - Bllvlt offentllf l8.01.72

Patent and Registration Board .... .........., _ ^. ,. . , (44) Nlhtlvlkslpsnon Jt kuLlulkalsun pvm. -

Patents * and registers Ansttkan utlagd et al. * Krifun publlcerad 28.09.79 (32) (33) (31) Pyydstty etuoikeus— Begird prlorltet 17.07.7O Netherlands-Netherlands (NL) 701060¼ (71) Shell Internationale Research Maatschappij N.V. , Carel van Bylandt-laan 30, The Hague, The Netherlands (NL) (72) Arie Cor Piet, Amsterdam, Cornells Ouverkerk, Amsterdam, The Netherlands (NL) (74) Oy Kolster Ab (5 ^) Method of the Claus process The present invention relates to a method for reducing the total sulfur content of the exhaust gases of a Claus process.

A process for preparing elemental sulfur from hydrogen sulfide by partially oxidizing it with oxygen or an oxygen-containing gas such as air and then reacting the sulfur dioxide formed from the hydrogen sulfide with the remaining hydrogen sulfide moiety in the presence of a catalyst is known as the Claus process. This process, which is often used in oil refineries and for the further processing of hydrogen sulphide from natural gas, is carried out in a Claus plant comprising a combustion chamber followed by one or more catalyst layers and one or more condensers installed between them, where the reaction products are cooled and the liquid separated. broken is recovered. The different process steps can be represented by the following reaction equations: 2H2S + 302 -> 2H2O + 2SO2 (1) 4H2S + 2SO4 = * 4H2 <) + 6/1 Sx (2) while the total reaction is represented by Equation (3): 2 56320 6h2s ♦ 302fcs6h20 + 6 / Sx (3)

At temperatures below 500 ° C, the value of x in the above equations is 8.

Since the catch of recovered elemental sulfur with respect to the hydrogen sulphide fed is not completely quantitative, a certain amount of unreacted hydrogen sulphide and sulfur dioxide is removed from the Claus process with its exhaust gases. These gases are normally burned in a furnace - as a result of which all the hydrogen sulphide is converted into sulfur dioxide and then released into the outside air through a high chimney. The amount of sulfur recovered depends to some extent on the total number of catalyst layers used in the Claus process. In principle, 98% of the sulfur can be recovered by using three layers.

In the light of the equally stringent requirements for reducing air pollution, the treatment of Claus exhaust gases in this way is less desirable. In addition, it involves certain losses in sulfur yield.

The present invention provides a method for effectively reducing the sulfur content of Claus exhaust gases or, more generally, exhaust gases from Claus-type processes, as a result of which the recovery of the recovered sulfur is considerably improved. In particular, the present invention provides a method of treating Claus exhaust gases which contain a relatively large amount of carbon dioxide in addition to hydrogen sulfide.

According to the present invention, sulfur and / or sulfur compounds are removed from the exhaust gases containing hydrogen sulfide, sulfur dioxide and / or elemental sulfur in the Claus plant, and the process is characterized in that the sulfur dioxide and / or elemental sulfur in the exhaust gases are converted to hydrogen sulfide by at a temperature together with a gas containing hydrogen and / or carbon monoxide over a sulfur-treated Group VI and / or Group VIII metal catalyst supported on an inorganic oxide support, after which the treated exhaust gases are passed to a regenerative at a temperature of more than 1,0 m / s, calculated at a temperature of 1 + 0 ° C or lower in relation to the surface of the air-conditioned base, and the non-absorbable part of the exhaust gases is led to the open air before being burned, if desired, and that the hydrogen sulphide-absorbent is regenerated and reused for the absorption of hydrogen sulfide and the hydrogen sulfide-rich gas mixture liberated in the regeneration is fed to the Claus plant.

In this application, Claus exhaust gases are understood to mean the residual gases obtained after the last catalyst bed of the Claus plant. Claus processes using two catalyst layers are usually used, but a third catalyst layer is also often used. Exhaust gases of this type contain not only hydrogen sulfide and sulfur dioxide in a ratio of about 2: 1 but also sulfur, oxygen, nitrogen, and small amounts of inert gases if the Claus process is operated with air, 3,56320 water, steam, carbon dioxide and small amounts of carbon monoxide, carbonyl sulfide carbon disulphide. These exhaust gases can also be obtained from the Claus process, which uses an insufficient amount of oxygen compared to the stoichiometric amount.

Once the Claus exhaust gases have been passed through the last catalyst bed and the relevant condenser to recover the elemental sulfur, its temperature is normally 130-170 ° C. However, in the reduction step above the Group VI and / or Group VIII metal catalyst, the temperature of the exhaust gases must be higher and therefore these exhaust gases are first heated to a temperature above 175 ° C. The temperature of the Claus exhaust gases is preferably raised to a temperature between 180-350 ° and most preferably between 200-300 ° C.

Raising the temperature above 175 ° C is also important given that the exhaust gases contain small amounts of elemental sulfur in the form of a mist. This detectable sulfur mist disappears when the temperature is raised above the dew point of the sulfur. It has also been found that as a result of raising the temperature above 175 ° C and preferably above 10 ° C in the presence of elemental sulfur in the gas phase, there is no detrimental effect on the catalytic activity of the reduction catalyst used.

When the Claus exhaust gases are heated to a temperature above 175 ° C, they are passed together with hydrogen or a hydrogen-containing gas over a sulfur-treated Group VI and / or Group VIII metal catalyst to reduce sulfur dioxide and hydrogen sulphide. At the same time, elemental sulfur is converted to hydrogen sulfide. The reduction catalysts used may be catalysts containing molybdenum, tungsten and / or chromium as a Group VI metal and preferably an iron group metal such as cobalt, nickel and / or iron as a Group VIII metal. The inorganic oxide support may be alumina, silica, magnesium oxide, boron trioxide, thorium oxide, zirconia, or a mixture of two or more thereof. Suitable reduction catalysts for use in the process of this invention include Ni / Mo / Al 2 O 3 or Co / t 10 / AlgO.

The Group VI and / or Group VIII metal catalyst is used in sulfide form. The preparation of the sulfide can be carried out in advance by means of a suitable sulfide-forming agent such as a mixture of hydrogen and hydrogen sulfide containing 10 to 15 v / v of hydrogen sulfide. It is also possible to form the sulfide of the catalyst in the process itself by means of Claus exhaust gases themselves. However, a sulfide-forming mixture containing hydrogen, hydrogen sulfide and water in a ratio of 1: 1: 1 with a reaction temperature of 300 to 100 ° C is particularly suitable. The sulfide-forming catalyst may contain Group VI and / or Group VIII metals as an oxide or element.

The treatment of the exhaust gases with a gas containing hydrogen and / or carbon monoxide is preferably carried out at a temperature between 180-350 ° C and more preferably between 200-300 ° C. Although the pressure used is mainly normal pressure, slightly elevated pressures can also be used if desired. The gas flow rate per hour used during the reduction is 500-10,000 N1 Claus exhaust gases per 4 56320 liters of catalyst.

The gas containing hydrogen and / or carbon monoxide used may well be a gas containing both compounds, such as city gas, water gas, synthesis gas, etc. Pure hydrogen or carbon monoxide may also be used. Suitable hydrogen-rich gases or gas mixtures are the exhaust gases from the catalytic reforming unit, the gas produced in the hydrogen plant or the gas obtained from the process units of saturated crude gases produced from petroleum.

The hydrogen-containing gas preferably contains at least 20 vol-56 or an equivalent amount of hydrogen and / or carbon monoxide. The amount of hydrogen or hydrogen-containing gas used is such that the ratio of hydrogen to sulfur dioxide oh is between 3: 1 and 13: 1 * This ratio is preferably between 3 * 5: 1 and 8: 1,

The above ranges remain the same when gas mixtures containing both hydrogen and carbon monoxide are used, and when carbon monoxide alone is used, since carbon monoxide corresponds to hydrogen. If elemental sulfur is also present in the Claus exhaust gases, the required amount of hydrogen and / or carbon monoxide can be calculated as a percentage of the elemental sulfur in Sod.

When CO is used as a reducing agent, some carbonyl sulfide is also formed. If the presence of OCS in the gas to be treated is not desirable, this carbonyl sulfide, as is known, can be decomposed by passing said gas at an elevated temperature over a layer of alumina.

The liquid used and the sulfur carbon absorbent to be regenerated are preferably an aqueous solution of an amine or a substituted amine. Absorbents of this type are well known in the art, such as alkali metal salts of dialkyl-substituted amino acids, e.g. dimethylamine potassium acetate and alkanolamines. More specifically, a polyalkanolamine such as di- or triethanolamine or dipropanolamine is used.

Alkanolamines are preferably used in aqueous solutions at molar concentrations of 8.3 to 3 and more preferably between 1 and 3 relative to said alkanolamines. After absorption, the hydrogen sulfide-containing absorbent is regenerated by heating and / or evaporation to give a hydrogen sulfide-containing gas mixture and a regenerated absorbent which can be reused. However, since regeneration is never complete and carbon dioxide can accumulate in the absorbent, especially if the Claus exhaust gases have a high concentration, these gases, after being treated with a gas containing hydrogen and / or carbon monoxide as described above, are preferably contacted with abrasive hydrogen sulfide. to increase selectivity and thereby reduce the rate of solvent recycling in combination with an aqueous alkanolamine solution at low temperature when high gas bump rates are used, said contact taking place in an absorption column having up to 20 or preferably less than 20 contact bases.

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Even more preferably, the absorption column has 4-5 contact bases. The gas flow rate used is at least m / s and preferably 2-4 m / s. These flow rates are based on an "active" or gas-flushed bottom surface. The low absorption temperature improves the selectivity of the hydrogen sulfide and carbon dioxide separation. The temperature is preferably below 40 ° C; the most satisfactory results are obtained at temperatures between 5 and 30 ° C. The Claus exhaust gases are contacted with an aqueous solution of alkanolamine at normal or near normal pressure. The contact is preferably made using the countercurrent principle. In some cases, the solvent recycle time can be further reduced by performing hydrogen sulfide removal to the maximum psax in the contact bottom column and the rest in venturi scrubbers with a relatively small amount of solvent, which may be completely different in temperature, nature, and composition.

Very good results are obtained by using diisopropanolamine as an absorbent.

When the absorbent is permeated, the unabsorbed part of the exhaust gases, which consists mainly of nitrogen and carbon dioxide and, in addition, very small amounts of hydrogen and hydrogen sulfide, is removed to the outside air. If desired, this non-absorbable part can also be incinerated in such a way as to be introduced into the chimney.

BEdcLvetjkajkaevä, which is released during the regeneration of the absorbent and which also contains carbon dioxide and water, is first cooled to condense the water therein. Normally, at least a portion of this water is recycled to the regeneration step to maintain the water content of the aqueous absorbent at the required level. After cooling, the hydrogen sulfide-containing gas is passed to a Claus plant to recover elemental sulfur from the gas. Since the process of this invention is used for Claus exhaust gases, it is most convenient to recycle the hydrogen sulfide gas obtained in the regeneration to the same Claus plant.

Figure 1 shows a flow chart for the reduction of Claus exhaust gases and the subsequent absorption of hydrogen sulfide, with the absorber recovery section forming part of the overall scheme.

Figure 2 shows a modified diagram in which said regeneration section forms part of an absorption regeneration section located before the actual Claus plant and in which the absorption of hydrogen sulphide after the reduction of the Claus exhaust gases takes place by means of a side flow from this section.

Referring to Figure 1, the number 1 denotes the line along which the exhaust gases from the Claus plant are fed. These gases, which have a temperature of 150 ° C, are heated by means of a heat exchanger 2 and passed over a reduction catalyst at 225 ° C to a reactor 3 * along line 4 and are cooled in a heat exchanger 5. At a temperature of 30 ° C, the exhaust gases enter an absorption column 6, e S 6 3? 0 which contains a liquid and regenerable hydrogen sulfide absorber. If desired, a condenser can be installed between the heat exchanger 5 and the absorption column 6 to remove any water in the exhaust gases. The non-absorbable components of the exhaust gas »consisting mainly of QO 2 and nitrogen» are removed along line 7. In order to convert all the hydrocarbon and sulfur carbon residues, the remaining gas is heated in the heat exchanger 8 and burned at 400 ° C in the incinerator 9 before it is led to the chimney along the line 10.

The hydrogen sulfide-containing absorbent is passed along line 11 to a desorption column 13 for regeneration. The regenerated absorbent is returned to the absorption column 6 via line 15, while the liberated hydrogen sulfide, which contains relatively small amounts of carbon dioxide, is passed to the Claus plant via line 17.

In the absorption column 13, the absorbent is regenerated at an elevated temperature by heating it with steam fed along a line 14. Since the regenerated absorbent is used at a low temperature, it is used in a heat exchanger 12 to heat the regenerated absorbent and then cooled in the condenser 16. The hydrogen sulfide-containing gas removed along line 17 is cooled in condenser 18 to condense any entrained water vapor; the condensed water is returned to the desorption column via line 19.

In Figure 2, the corresponding parts are denoted by the same reference numerals. In the additional scheme, a gas stream rich in hydrogen sulfide is fed along line 24 to an absorption column 23 containing regenerable hydrogen sulfide absorber. The gas stream containing only a small amount of hydrogen sulfide is removed along line 25, while the absorber containing hydrogen sulfide is removed along line 26 to a desorption column 13 for regeneration. Lines 26 and 11 (in absorption column 6) merge at point B and lead to column 13 as common line 11. The regenerated absorbent is removed along line 15 and used in a heat exchanger 12 to heat the regenerated absorbent. After the radiator 16, the line 15 branches at A; the side stream of regenerated absorber passes along line 15 of the absorber column 6 where it comes into contact with the reduced Claus exhaust gases. The main current returns to the absorption column 23 via line 22.

The hydrogen sulfide released from the absorbent in the regeneration is cooled in a condenser 18 to remove water and returned to the Claus plant, shown schematically at number 20. The exhaust gases from this Olaus plant are removed along line 1 and treated as indicated with reference to Figure 1.

The process of the present invention is particularly suitable for the treatment of Claus exhaust gases which, in addition to hydrogen sulfide, contain a relatively large amount of carbon dioxide. The amount of carbon dioxide contained in these exhaust gases can exceed 5 vol- $ and can be e.g. 8-15 vol- $ without causing technical difficulties 7 '> 6320 or economic disadvantages in the use of the process.

The invention is further illustrated by the following examples.

Example 1

The synthetic Claus exhaust gas was reduced to the sulfide form

Over a Co / Mo / Al 0 O (3.2 parts by weight of Co / 13 → 4 parts by weight of Mo / 100 parts by weight .23 A 2 O 2) using a mixture of hydrogen and carbon monoxide. Synthetic Claus exhaust gas with varying sulfur dioxide content was passed over the catalyst together with the reduction gas at a volume flow rate of 1700 N1 gas / l catalyst / h. The composition of the whole mixture was SO2 ranged from H2 0.5-0.6 vol .- $ CO 0.3-0.4 vol .- $> H2S 1.2 vol.-96 rest

The catalyst was used in the form of particles with a size of 0.3-0.6 mm (3Ο-5Ο mesh).

The conversion of the catalyst to sulfide took place at a maximum temperature of 375 ° C and a pressure of 10 kg / cm 3 using a Hg / HgS gas mixture containing 12.5 vol. Of hydrogen sulfide. The temperature was raised stepwise from a room temperature of 4 hours to 375 ° C (first hour from 20 ° C to 100 ° C; second and third hours from 100 ° C to 250 ° C and fourth hour from 250 ° C to 375 ° C). C a). After sulfide formation, the catalyst was cooled to 100 ° C by continuously feeding a gas mixture containing said hydrogen sulfide; then only hydrogen gas was lowered and finally the reduction of the Claus exhaust gas was started. The experiment was performed at different reduction temperatures. The results obtained are summarized in Table A.

Table A

SO2 ~ concentration Reaction- Conversion # SO2 concentration in the gas mixture temperature H2 CO H2 + CO after reduction vol .- $ (feed) o ^, ^ vol.-i 0.17 222 34 65 45 0.001 0.17 250 27 100 50 0.001 0.36 250 63 100 80 0.03 0.36 280 89 100 94 0.001

Example 2

Synthetic Claus exhaust gas, which in addition to sulfur dioxide and hydrogen sulfide also contained a small amount of gaseous elemental sulfur, was reduced with hydrogen at 220 ° C using the same sulfide form Co / Mb / Al 2 O 2 catalyst as used in the experiments of Example 1. The exhaust gas was passed over said catalyst together with hydrogen at a volume flow rate of 1400 N1 gas / liter of catalyst / h. The composition of the entire gas mixture before and after reduction is shown in the following table.

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Composition of the gas, before reduction After reduction Vol .- # S02 Ο, ΙΘ 0.002 S0 0.018 H2 1.5 0.8

h20 29 JO

h2s 1.3 1.7

Ng rest rest

The total conversion calculated based on the hydrogen consumed is 45 #.

Example 3

The synthetic Claus exhaust gas was reduced with carbon monoxide over the same sulfide form Co / Mo / AlgO 2 catalyst used in the two previous examples. The reduction temperature was 230 ° C, while the total volume flow rate of the exhaust gas and carbon monoxide was 1700 Nl / l catalyst / h. The composition of the whole gas mixture before reduction was as follows: SO2 0.4 vol- # CO 1.2 vol- # H2O 30 vol- # H2S 1.2 vol- #

Ng rest

The conversion calculated on the basis of carbon monoxide consumed was 35 #.

When the above experiment was repeated at a gas volume flow rate of 900 Nl / l / h at the same reduction temperature, the conversion was 90 #.

Example 4

The carbon dioxide-rich Claus exhaust gas was reduced with hydrogen over a sulfide-containing Co / Mo / Al 2 O 2 catalyst at 220 ° C. The composition of the resulting gas after reduction was as follows: H2S 2.5 vol .- # CO2 11.1 vol .- # H2 0.6 vol .- # N2 85.8 vol .- #

A gas having the above composition. Passed at a rate of 2 m / e through a column containing 11-12 bottoms And In which a solution of diisopropanolamine with water 27 p- # was circulated. The temperature of the D1-alkaliamine before it came into contact with the hydrogen sulfide-containing gas was 20 ° C in one case and 40 ° C in the other. The composition of the treated gas after passing through the diisopropanolamine solution and the composition of the hydrogen sulfide-containing gas obtained after regeneration to said amine class are shown in the following table.

The treated gas was finally fed to a waste incinerator and the hydrogen sulphide gas was returned to the Claus plant, from which the exhaust gases originated.

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It can be seen from the results of the experiment that when the conditions of the process of this invention are used, hydrogen sulfide is absorbed very selectively, even in the presence of high CO 2 concentrations.

Example 5

A gas mixture containing 2.57 v / v H 2 S and 10.58 v / v CO 2 was contacted in a bottom column under no conditions with an aqueous solution of diisopropanolamine which was 2 molar with respect to the amine. The conditions for temperature, gas flow rate, number of column bottoms, and solution dispersion height at these bottoms were changed so that the hydrogen sulfide concentration in the treated gas was 0.05 vol.

The results are shown in Table C below

Table C

Temperature Gas Dispersion Bottom Solution Treated gas flow altitude / number m / kmol HgS 00 ^ ° C velocity * bottom, * 2S vol. # # Vol. # # M / sx cm in gas 30 1.0 10 6 2.48 0.05 8.47 30 1.5 10 9 2.20 0.05 8.89 30 2.5 10 15 1.97 0.05 9.45 20 2.5 20 7 1.59 0.05 9 50 50 2.5 20 7 2.11 0.05 9.17 40 2.5 20 7 2.82 0.05 8.70 x with respect to the bottom area of the gas purge.

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From the data collected, it can be concluded that it is preferable to operate at low temperatures at relatively high gas flow rates using a relatively high dispersion height at the bottom of the column; this ensures that the highest possible selectivity for hydrogen sulphide absorption is achieved when using relatively small amounts of solution.

Claims (7)

12 56320 A method for removing sulfur and / or sulfur compounds from exhaust gases containing hydrogen sulphide, sulfur dioxide and / or elemental sulfur in a Claus plant, characterized in that the sulfur dioxide and / or elemental sulfur contained in the exhaust gases are converted to hydrogen sulphide by condensing the exhaust gases together at 180-350 ° C. with a gas containing hydrogen and / or carbon monoxide over a sulphide-shaped Group VI and / or Group VIII metal catalyst on an inorganic oxide support, after which the exhaust gases thus treated more than 1,0 m / s calculated at or below 1 + 0 ° C above the surface of the air-conditioned base, and the unabsorbed part of the exhaust gases is vented to the outside air before being burned, if desired, and distant to the hydrogen sulfide absorption and the hydrogen sulfide-rich gas mixture released during regeneration is led to the Claus plant. Process according to Claim 1, characterized in that the exhaust gases are passed over the sulphide catalyst at a temperature of 200 to 300 ° C. Method according to Claim 1 or 2, characterized in that the exhaust gases are passed through the absorbent at a gas velocity of at least 1.5, preferably 2 k k / s, relative to the surface of the air-conditioned base. U. Method according to one of Claims 1 to 3, characterized in that the absorption column contains a U-15 contact base. Method according to one of Claims 1 to U, characterized in that, after the exhaust gases have passed through the absorption column, they are again brought into contact with the liquid, regenerable absorber in a venturi scrubber. Method according to one of Claims 1 to 5, characterized in that the gas containing hydrogen and carbon monoxide contains at least 20% by volume of? hydrogen. Method according to one of Claims 1 to 6, characterized in that the hydrogen sulfide-rich gas liberated from regeneration is fed to the Claus plant from which the exhaust gases leave.